/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Lucene.Net.Index;
using Lucene.Net.Util;
namespace Lucene.Net.Search.Highlight
{
/// Utility class used to extract the terms used in a query, plus any weights.
/// This class will not find terms for MultiTermQuery, RangeQuery and PrefixQuery classes
/// so the caller must pass a rewritten query (see Query.rewrite) to obtain a list of
/// expanded terms.
public static class QueryTermExtractor
{
/// Extracts all terms texts of a given Query into an array of WeightedTerms
///
///
/// Query to extract term texts from
///
/// an array of the terms used in a query, plus their weights.
///
public static WeightedTerm[] GetTerms(Query query)
{
return GetTerms(query, false);
}
/// Extracts all terms texts of a given Query into an array of WeightedTerms
///
///
/// Query to extract term texts from
/// used to compute IDF which can be used to a) score selected fragments better
/// b) use graded highlights eg chaning intensity of font color
/// the field on which Inverse Document Frequency (IDF) calculations are based
/// an array of the terms used in a query, plus their weights.
public static WeightedTerm[] GetIdfWeightedTerms(Query query, IndexReader reader, string fieldName)
{
WeightedTerm[] terms = GetTerms(query, false, fieldName);
int totalNumDocs = reader.NumDocs();
foreach (WeightedTerm t in terms)
{
try
{
int docFreq = reader.DocFreq(new Term(fieldName, t.Term));
// docFreq counts deletes
if (totalNumDocs < docFreq)
{
docFreq = totalNumDocs;
}
//IDF algorithm taken from DefaultSimilarity class
var idf = (float)(Math.Log((float)totalNumDocs / (double)(docFreq + 1)) + 1.0);
t.Weight *= idf;
}
catch (IOException e)
{
//ignore
}
}
return terms;
}
/// Extracts all terms texts of a given Query into an array of WeightedTerms
/// Query to extract term texts from
/// true to extract "prohibited" terms, too
/// The fieldName used to filter query terms
/// an array of the terms used in a query, plus their weights.
public static WeightedTerm[] GetTerms(Query query, bool prohibited, string fieldName)
{
var terms = new HashSet();
if (fieldName != null)
{
fieldName = StringHelper.Intern(fieldName);
}
GetTerms(query, terms, prohibited, fieldName);
return terms.ToArray();
}
/// Extracts all terms texts of a given Query into an array of WeightedTerms
///
///
/// Query to extract term texts from
///
/// true to extract "prohibited" terms, too
///
/// an array of the terms used in a query, plus their weights.
///
public static WeightedTerm[] GetTerms(Query query, bool prohibited)
{
return GetTerms(query, prohibited, null);
}
//fieldname MUST be interned prior to this call
private static void GetTerms(Query query, HashSet terms, bool prohibited, string fieldName)
{
try
{
if (query is BooleanQuery)
GetTermsFromBooleanQuery((BooleanQuery) query, terms, prohibited, fieldName);
else if (query is FilteredQuery)
GetTermsFromFilteredQuery((FilteredQuery) query, terms, prohibited, fieldName);
else
{
var nonWeightedTerms = Support.Compatibility.SetFactory.CreateHashSet();
query.ExtractTerms(nonWeightedTerms);
foreach (var term in nonWeightedTerms)
{
if ((fieldName == null) || (term.Field == fieldName))
{
terms.Add(new WeightedTerm(query.Boost, term.Text));
}
}
}
}
catch (System.NotSupportedException ignore)
{
//this is non-fatal for our purposes
}
}
/// extractTerms is currently the only query-independent means of introspecting queries but it only reveals
/// a list of terms for that query - not the boosts each individual term in that query may or may not have.
/// "Container" queries such as BooleanQuery should be unwrapped to get at the boost info held
/// in each child element.
/// Some discussion around this topic here:
/// http://www.gossamer-threads.com/lists/lucene/java-dev/34208?search_string=introspection;#34208
/// Unfortunately there seemed to be limited interest in requiring all Query objects to implement
/// something common which would allow access to child queries so what follows here are query-specific
/// implementations for accessing embedded query elements.
///
private static void GetTermsFromBooleanQuery(BooleanQuery query, HashSet terms, bool prohibited, string fieldName)
{
BooleanClause[] queryClauses = query.GetClauses();
for (int i = 0; i < queryClauses.Length; i++)
{
if (prohibited || queryClauses[i].Occur != Occur.MUST_NOT)
GetTerms(queryClauses[i].Query, terms, prohibited, fieldName);
}
}
private static void GetTermsFromFilteredQuery(FilteredQuery query, HashSet terms, bool prohibited, string fieldName)
{
GetTerms(query.Query, terms, prohibited, fieldName);
}
}
}